If the new currency unit the SDR is used only for international settlements and reserves it may be successful. However, if it is promoted as a general currency for domestic usage, then one only has to look at the current troubles in Europe to understand what a trap this is.
Unity of currency without unity of government and fiscal policy and taxation is difficult if not impossible to maintain. One world currency is the step to one world government. And those who control the currency will, almost inevitably, control the people of the world.